Multi-Channel Phase Calibration Method for 5G Phased Array System

Cemin Zhang, PhD

Chengdu Sicore Semiconductor Ltd.

Outlines

• 5G phased array – why phase accuracy is the key

• Analog phase shifters for 5G

• Challenges for Multi-channel phase calibration

• Proposed phase calibration method for 5G phased array

• Results and conclusions

5G Beamforming and MIMO

Phased Array 2x2 and mxn Channel

• More channel/element means sharper beam and higher gain;

• Demands higher phase shift accuracy;

• Some 5G testbed, 128 x 128 array are proposed.

ANT1 ANT2

ANT3 ANT4

…

… …

…

…

…

…

…

1 to n

1 to

m

m x n channel 2 x 2 channel

Phased Array Transceiver Architecture

• Key components: Phase shifter, Attenuator

• Key specs: Channel phase consistency, insertion loss

ANT

Tx

Rx

PA PS ATT

LNA PS ATT SPDT

Ideal multi-channel phased-array

A) Each channel, w. same control word:

• Identical phase shift amount

• Identical attenuation amount

B) Phase stays constant when attenuation state changes, and vice versa

Actual multi-channel phased-array

A) Each channel, w. same control word:

• Phase shift amount non-identical

• Attenuation amount non-identical

B) Phase changes when attenuation state changes, and vice versa

Traditionally, need full calibration for each channel.

Phase Shifter – Analog vs. Digital

Analog Phase Shifter Digital Phase Shifter

Insertion Loss Lower Higher

Freq Bandwidth Wide Narrow

Phase Resolution < 1° (limited by DAC) 5.625° (for 6bit)

Monotonic Response Yes No

Bias Requirement Single positive voltage Need negative bias

IP3 Lower Higher

Multi-channel Phase Calibration Ready

Yes No

Analog Phase Shifter Work w. DAC

• DB0~DB7: Digital control word from MCU

• Vref: ref voltage for DAC

• Vt = D • (Vref), for 8-bit DAC，D = 0 to 255/256.

DAC (8-bit) MCU

1

2

3

4

7 8 9 10

NC

GND

RFIN

GND

NC NCNC

5

6

NC

NC

11 12

18

17

16

15

NC

GND

RFOUT

GND

14

13

NC

NC

NC NCNC

24 23 22 21 20 19

NC NCNC VT NCNC

DB0~DB7

control Vt

Vref

ROM

Sicore MMIC Product Lines

VCO

LO IF RF

Mixers

/N

Freq Div Phase Shifter Equalizer BPF

24G TRX Switches ATT Amp

QFN Plastic

Die QFN Ceramic Evaluation Kits

Sicore 5G Portfolio

website: www.sicoresemi.com EDI Booth #: 605

http://www.sicoresemi.com/

SIP052 Analog Phase Shifter – SPECS

Measured Results

Frequency (GHz)

Ph

ase

sh

ift (d

eg

)

Frequency (GHz) Frequency (GHz)

Inse

rtio

n L

oss (

dB

)

Re

turn

Lo

ss (

dB

)

Analog Phase Shifter Product Line：1 – 31.5GHz

0 5 10 15 20 25 30 35

SIP012SP4

SIP013SP4

SIP014SP4

SIP015SP4

SIP016SP4

SIP017SP4

SIP050SP5

SIP051SP5

SIP052SP5

SIP054SP3

Frequency Coverage（GHz）

Ultra-wideband APS 180 deg Wideband APS 360 deg

Measured Phase Shift Distribution

3-6GHz phase shift amount distribution from a same batch lot at Vt=14V.

Need for Innovated Channel Phase Calibration !

a cyclic convergence process using the regression algorithm to continuously adjust the

phase and attenuation amount for each state of the channel.

Multi-channel Phase Calibration Steps

1. Reference channel – full calibration

2. Fast calibration for the rest channels based on REF channel calibrated data

Phase shift vs. Vt - different channels @4.5GHz

Channel B, phase shift PB

Channel C, phase shift PC

Ref Channel

A,

phase shift PA

Ph

ase

sh

ift fr

om

diffe

ren

t ch

an

ne

l (d

eg)

Channel Phase Calibration Steps @4.5GHz

Phase Shift Error of Channel B Compared to Channel A

Phase Shift Error of Channel C Compared to Channel A

Reference Channel A

DAB=PB-PA

DAC=PC-PA

Calibration Function F(DAB)

Calibration Function F(DAC)

Vt (V)

0 1 2 4 5 6 7 8 9 10 11 12 3 13 -6

-4

-2

0

2

4

6

Initia

l P

ha

se

sh

ift E

rro

r (d

eg

)

0

Phase shift error after calibration @4.5GHz

Phase shift error after calibration (channel

B)

Phase shift error after calibration (channel

C)

Vt (V)

0 1 2 4 5 6 7 8 9 10 11 12 3 13

0

Ph

ase

sh

ift E

rro

r (d

eg

)

0.5

-0.5

-1

-1.5

1

1.5

Channel Phase Calibration Steps: more sections/anchor points

Phase Shift Error of Channel B Compared to Channel A

DAB2=PB2-PA2

DAC2=PC2-PA2

Calibration function

F1(DAB1)

Phase Shift Error of Channel C Compared to Channel A

DAB1=PB1-PA1

DAC1=PC1-PA1

Calibration function F2(DAB2)

Calibration function

F1(DAC1)

Calibration function F2(DAC2)

Vt (V)

0 1 2 4 5 6 7 8 9 10 11 12 3 13 -6

-4

-2

0

2

4

6

Initia

l P

ha

se

sh

ift E

rro

r (d

eg

)

Reference Channel A

Phase Shift vs Frequency – different channel @Vt=13V

Channel B

Channel C Ref channel A

• Phase shift difference stays constant over frequency

• Calibrate at a single frequency (e.g. @4.5GHz), apply to full frequency band.

Ph

ase

sh

ift @

Vt=

13

V, ch

an

ne

l A,

B,

C (

de

g)

Frequency (GHz)

Channel B，4.5GHz Channel B，3GHz

Channel B，6GHz

Channel C，3GHz Channel C，4.5GHz Channel C，6GHz

Phase shift error after calibration @3, 6GHz

Ph

ase

sh

ift E

rro

r (d

eg

)

Conclusions

• Proposed a novel phase calibration method for multi-channel 5G phased-array

• Achieved lowest time, data space consuming, while keeping precision of

References

• B. Peterson et al., "5G Fixed Wireless Access Array and RF Front-End Trade-Offs", Microwave Journal, Feb. 2018.

• Microwave Journal webinar: Design Innovations in 5G mmWave FEMs and Phased Arrays

• SIP052SP5 product datasheet. [Online]. Available: http://www.sicoresemi.com.

• www.mitsubishielectric.com: Massive-element antenna systems technology for 5G base stations

http://www.sicoresemi.com/

Thanks!

Q & A